Question

Which of the following is incorrect during amphimixis?
A. Swelling of sperm nucleus
B. Initial movement of male nucleus along copulation path
C. Establishment of achromatic spindle by proximal centriole
D. completion of second meiotic division if not occurred already

Answer 1

Hint: Amphimixis – It is the sexual reproduction involving the fusion of two different gametes to form a zygote. It combines the genetic information from two parents.

Complete Answer:
Fertilization in humans complete in steps –
1. Acrosomal reaction
2. Cortical reaction
3. Amphimixis

1) Acrosomal reaction and cortical reaction plays key roles in sperm entry into egg (ovum). The sperm entry stimulates the egg (secondary oocyte) to resume and complete the suspended meiosis-II, which produces haploid mature ovum and a secondary polar body.
2) At this time the head of the spermatozoon, which consists of the nucleus, separates from the middle piece and the tail absorbs water and swells up and becomes the male pronucleus.
Second polar body and sperm tail degenerates the establishment of achromatic spindle by proximal centriole and second meiotic division is done after the fusion of male and female gametes.
3) Mixing up of the chromosomes of spermatozoan and an ovum is called amphimixis (or karyogamy). This completes the fertilization. Achromatic fibre arose in cytoplasm and is elastic in nature. Astral rays arise from the centriole and radiate out. Spindle fibres extend between two asters.

The correct option is B.

Additional Information:
- Amphimixis is a synonymous term used for sexual reproduction.
- Amphimixis cannot be confused with automixis or apomixis, which are both associated with sexual reproduction.

Note: Neck of sperm contains two centrioles lying one behind and at right angles to the other. The proximal centrioles play an important role in the first cleavage of the zygote. A distal centriole gives rise to the axial filaments of the sperm.